Human PLXNB2 variants (MIM*604293) and aberrant PLXNB2 expression have been associated with lung cancer,14 15 acute myeloid leukaemia,16 amyotrophic lateral sclerosis,17 glioblastoma,18 autism spectrum disorders with regression,19 psoriasis20 and first trimester euploid miscarriage.21 In contrast, despite the apparent importance of plexins in development, only biallelic PLXND1 (MIM*620282) and PLXNA1 (MIM*601055) variants have so far been associated with Mendelian genetic disease in humans. Here, PLXNB2 is linked to autism spectrum disorder.